Those lines started as early as 4:30 a.m. across Kansas City, voters showing up in the dark with chairs, books and plenty of coffee outside of polling places.

About 500 people were lined up at the St. James Methodist Church near downtown when the polls opened at 6 a.m., and another 500 or so stood in line outside Kansas City's University Academy High School when polls opened there.

Raytown resident Norma Storms, 78, said hundreds of voters converged on four polling places near her house, filling the parking lots of Westridge Elementary School and Westridge Christian Church, even her driveway.

"I have never seen anything like this in all my born days," she said. "I am just astounded."

Voter turnout was just as strong around St. Louis, with long lines forming across the area well before dawn.

Secretary of State Robin Carnahan has projected a near-record turnout: 76 percent of the state's 4.2 million registered voters. That group could include more than 300,000 people who have registered since the beginning of the year, one-third of whom enrolled in the St. Louis region alone.

Only in 1992, when Bill Clinton won the first of his two terms in the White House, did a higher proportion of Missouri voters — 78 percent — cast ballots on Election Day. But should Carnahan's predictions hold true Tuesday, the actual number of voters this year would be greater.

State and local election officials have hired more temporary workers, repeatedly tested electronic voting machines, printed more paper ballots and taken other precautions in anticipation of the high turnout. Outside experts have touted Missouri's preparations.

But if the past two presidential elections are any indication, post-election challenges to the voting process could await.

In 2000, a state judge ruled on Election Day that polls in the city of St. Louis remain open for three hours past the scheduled closing because of long lines and other problems. Forty-five minutes into that extended time, a federal appeals court shut down the polls.

Republicans quickly raised the specter of vote fraud in the overwhelmingly Democratic city. A subsequent state investigation found that at least 143 unregistered voters cast ballots in St. Louis, while an unknown number of properly registered voters were wrongly turned away.

After the 2004 presidential election, the federal Justice Department sued the state and Carnahan's office for alleged violations of a law governing when states must purge ineligible voters from registration lists.

A U.S. District Court judge in 2007 sided with the state, though a federal appeals court this past summer sent the dispute back to that trial judge. Missouri has since created a statewide voter registration database.